Package: libguestfs-tools
Version: 1:1.18.1-1+deb7u3
There is a typo in the man page of virt-resize:
# virsh dumpxml guestname | xpath /domain/devices/disk/source
should read:
# virsh dumpxml guestname | xpath -e /domain/devices/disk/source
See man page for xpath (libxml-xpath-perl).